linux-kernel - Re: xfstests 073 regression

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Date:	Tue, 2 Aug 2011 22:04:45 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: xfstests 073 regression

On Tue, Aug 02, 2011 at 07:44:28PM +0800, Wu Fengguang wrote:
> On Tue, Aug 02, 2011 at 12:52:42AM +0800, Christoph Hellwig wrote:
> > wb_check_background_flush is indeed what we're hitting.
> 
> That means s_umount is NOT held by another queued writeback work.

Right. We already kind of knew that was ocurring because there's
a remount,ro going on.

> 
> > See the trace output using a patch inspired by Curt's below:
> > 
> > # tracer: nop
> > #
> > #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> > #              | |       |          |         |
> >            <...>-4279  [000]   113.034052: writeback_grab_super_failed: bdi 7:0: sb_dev 0:0 nr_pages=9223372036854775807 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=wb_check_background_flush
> >            <...>-4279  [000]   113.034052: writeback_grab_super_failed: bdi 7:0: sb_dev 0:0 nr_pages=9223372036854775807 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=wb_check_background_flush
> >            <...>-4279  [000]   113.034052: writeback_grab_super_failed: bdi 7:0: sb_dev 0:0 nr_pages=9223372036854775807 sync_mode=0 kupdate=0 range_cyclic=1 background=1 reason=wb_check_background_flush
> 
> What's that bdi 7:0? And sb_dev=0:0, nr_pages=9223372036854775807=0x7fffffffffffffff.
> 
> All are indicating some special bdi/inode.

#define LOOP_MAJOR 7

It's a loop device. xfstests uses them quite a lot.

Maybe it would be a good idea to run xfstests on an xfs filesystem
in your regular writeback testing cycle to get decent coverage of
this case?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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